How to execute blender from python?
The easiest way would be to use the subprocess module to start Blender.

import subprocess

subprocess.run(["/path/to/blender", "somefile.blend"])



  Since python can be called from inside blender so it has to be possible vice versa.


This is not a very logical statement. Just because Blender embeds Python doesn't mean anything when it comes to starting Blender from Python.